This grant application for an early randomized surgical epilepsy trial (ERSET) was originally prepared with the help of planning grant R21 NS37897, awarded in recognition of the fact that mesial temporal lobe epilepsy (MTLE) is a surgically remediable syndrome, that surgical treatment for this disorder is underutilized, and that true equipoise exists concerning the relative benefits of surgery vs. continued treatment with new antiepileptic drugs, early in the course of the disorder. We now submit a revised proposal for a multicenter randomized controlled trial (RCT) to compare the efficacy of early surgical intervention for MTLE with continued optimal pharmacotherapy. The primary outcome measure will be freedom from disabling epileptic seizures (complex partial and secondarily generalized seizures, and simple partial seizures that are apparent to an observer). Patients aged 12 years and older with suspected MTLE will be candidates for recruitment if disabling seizures: 1) have not responded to two or more antiepileptic drugs, one of which must be either Dilantin, Tegretol, or Carbatrol, and 2) have not persisted, according to defined criteria, for more than two years. Fifteen epilepsy surgery centers spaced evenly across the country will actively recruit patients meeting these criteria. These patients will undergo a rigid presurgical evaluation protocol, standardized across centers, and 200 surgical candidates will then be randomized to either anteromesial temporal resection or two years of additional pharmacotherapy. Studies will test five hypotheses: 1) Surgical treatment will be more effective than medical treatment in reducingthe frequency and severity of epileptic seizures; 2) Surgical treatment will be more effective than medical treatment in improving quality of life; 3) Surgical treatment will be more effective than medical treatment in improving psychological and social function; 4) Morbidity and mortality associated with surgical treatment will be no greater than that associated with medical treatment; and 5) Progressive hippocampal atrophy and mesial temporal hypometabolism will occur only in patients who continue to have frequent complex partial and generalized tonic-clonic seizures.